Power converters/inverters are commonly used in a machine for motor control. Power converters/inverters usually include a plurality of power transistors, and these power transistors may be switched on and off to modulate an output voltage from the power converter/inverter. Examples of power transistors may include bipolar junction transistors (BJT), the Darlington device, metal oxide semiconductor field effect transistors (MOSFET), and insulated gate bipolar transistors (IGBT). In particular, IGBTs have been widely used in a wide range of applications due to its high switching speed and ability of conducting very high current.
High voltage power converters/inverters are usually expensive, and failure of power transistor components could be costly. Additionally, in the event that there is a malfunction in the power transistors or their wiring, damage may be caused to the other power components in the circuit. Therefore, it becomes highly desirable that any faults with power transistors, their driving circuit, and associated wiring are detected before high voltage is applied to the power converters/inverters. Furthermore, it may also be important to precisely and quickly locate the type of fault (e.g., a power transistor fault, an open circuit fault), and if possible, positions of the fault, and to disable the inverter/converter functionality once a fault is detected.
A method for diagnosing faults in IGBTs is described in U.S. Pat. No. 6,927,988 to Cheng et al. (“the '988 patent”). The '988 patent describes a method for detecting and locating a faulted IGBT using a load. In the method, the output of a power inverter is connected to a three-phase resistor load having a common resister value, and a voltage is applied on the power inverter. IGBTs are controlled such that certain currents flow across them, and the currents are measured and compared with their expected values. If the currents do not match their expected values, a fault may be detected and diagnosed.
Although the testing method described in the '988 patent may be effective for testing IGBT devices associated with a power inverter, it may be problematic. For example, the IGBT test described in the '988 patent requires that a power source be connected to the power inverter to supply power to the power inverter, and a circuit is formed to conduct a current flow among the power source, the power inverter, and a load. As a result, other power electronics components connected in the circuit as well as the load (for example, a motor) may be damaged due to IGBT failure and/or wiring faults. Thus, it may not be capable of detecting and locating a fault before high-voltage is applied. Furthermore, although the testing method described in the '988 patent may indicate whether a fault exists, it may be incapable of disabling the inverter/converter functionality, once a fault is detected.
The disclosed system and method for testing power transistors is directed towards overcoming one or more of the shortcomings set forth above.